The present invention relates to central control systems for monitoring the location of a plurality of trains within a transit system. More particularly, the present invention relates to a centralized electronic control system which utilizes interlocking circuits and false occupancy correction factors to monitor train locations.
Central tracking systems monitor a number of trains along a transit system by assigning train designators to individual trains and section designators to individual sections of the track throughout the transit system and by monitoring the occupancy of those track section by the various trains in the system. If a particular train is in a particular track section, that section is said to be occupied. The presence of a train within the section will trigger a sensor in the track, alerting the control system which will alert the central control computer that that portion of the track is occupied. However, it occasionally arises that a section of the track system will indicate occupancy when in fact that portion of the track system is not occupied, this is referred to as a false occupancy.
A false occupancy occurs when a track circuit signals an occupancy at a location where the central control system does not expect an occupancy to occur. In situations where track circuits on both sides of a newly received occupancy signal ere previously unoccupied, the control system does not expect an occupancy to occur. The central control system will therefore classify this type of an occupancy as a potential false occupancy.
A false occupancy can be caused by a variety of different factors, such as input/output (I/O) failure, signal wire failure or an external event that may cause a track to become shorted or the track circuit to become shorted. In a train control system with automatic train control, a false occupancy will not allow other trains to proceed through the falsely occupied section of track as long as the cause of the occupancy indication signal is unknown.
The methods utilized by existing track control systems present limitations in the presence of false occupancies. Once a false occupancy has been located at a particular track section, a train cannot be tracked through the section. The presence of the false occupancy will obscure tracking of the train. There is a maximum number of false occupancies that can be accommodated by a system. When a system becomes overloaded with a greater number of false occupancies, train tracking becomes impossible.